Progressive deterioration of myocardial function during acute and/or chronic heart disease probably involves defects in CA2+ uptake and release by the cardiac sacroplasmic reticulum (SR). It is vital, therefore, to develop an understanding of how the SR is regulated. Accordingly, this proposal will examine and elucidate the role of phosphorylation/dephosphorylation processes of SR in regulating its calcium pump both under in vitro and in vivo conditions. Work from several laboratories including ours has shown that SR function is modulated by cAMP-dependent phosphorylation. Recently, we have shown that cardiac SR is also phosphorylated by another intrinsic protein kinase which depends on calcium and calmodulin for its activity, and this phophorylation also appears to control Ca2+ transport. The proposed research will further elucidate the mechanism by which Ca2+-calmodulin-dependent phosphorylation regulates the Ca2+-ATPase activity and will determine the individual steps in the Ca2+-ATPase reaction sequence which are modulated by this phosphorylation. The interrelationship of cAMP-dependent and Ca2+-calmodulin-dependent phosphorylation as regulatory mechanisms for the Ca2+ pump will be studied. Special emphasis will be placed on the Ca2+-calmodulin-dependent protein kinase(s) and on the phosphoprotein phosphatase(s) in terms of purification and characterization since these are likely the enzymes involved in the "reversible regulation" of SR function in vitro. Furthermore, this proposal will correlate the more biochemical in vitro findings with in vivo events, where SR phosphorylation will be studied using 32P-perfuse beating hearts. The dynamics of changes in SR phosphorylation/dephosphorylation and function during the response of the myocardium to Beta-adrenergic agonists/antagonists will be determined. Changes in SR will be correlated with changes in other cellular functions which occur in response to Beta-adrenergic agonists. The specificity of such existing correlations will be determined. The proposed research should provide important information concerning phosphorylation/dephosphorylation of SR as a regulatory mechanism for the calcium pump and, therefore, an important mechanisms of the contraction-relaxation cycle in cardiac muscle. These basic studies will lead to more rational experiments designed to elucidate the role of SR phosphorylation/dephosphorylation in models of ischemic heart disease and congestive heart failure.